Mislow intermediate

Mislow and his co-workers (261) suggested, however, that epimeriza-tion of menthyl sulfinates occurs via either a sulfurane intermediate 221 or a sulfonium salt 222. 

Mislow s [2,3]-sigmatropic rearrangement of sulfoxides is more than a mechanistic curiosity, because the intermediate sulfenate 5.83 can be intercepted by a suitably thiophilic reagent, converting an enantiomerically enriched sulfoxide 5.82 into a comparably enriched rearranged allyl alcohol 5.84, with suprafacial shift 5.85 of the functionality. 

Vinyl sulfoxide isomerization followed by Mislow-Evans rearrangement was also central to a S5mthetic route toward the hydroazulene moiety of the antibiotic fungal metabolite guanacastepene A fScheme 18.611. In this case, a diastereomeric mixture of vinyl sulfoxides 241 resulted upon oxidation of the starting vinyl sulfide 240. Subsequent treatment with DBU led to the sequential isomerization/[2,31-rearrangement process. Under these conditions, the intermediate sulfenate was converted to the allylic alcohol 242, produced as a 4 1 mixture of epimers. Here, the modest selectivity in formation of the allylic stereocenter was of no synthetic consequence, as the alcohol was subsequendy oxidized to the corresponding enone. Notably, the overall conversion from 240 to 242 represents a 1,3-vinyl-to-allyl heteroatom transposition. 

An allylic halogen oxide [2,3]-sigmatropic rearrangement is another intriguing analogue of the Mislow-Evans process. In this scenario tScheme 1R.7QT oxidation of an allylic iodide provides iodoso intermediate 282, which rearranges to the corresponding allylic hypoiodite 283. Yamamoto et al. found that the reaction worked best with excess peracid oxidant, as the initially formed hypoiodite was further oxidized to the iodate ester (284), an intermediate... 

The alkylation of 38 with menthyl chloroacetate produced a diastereomeric mixture of phosphine oxides 39 and 39. These mixtures could be separated into individual diastereomers in 10 1% yields by fractional recrystallisation in hexane. Each epimer was subjected to hydrolysis to the corresponding acid and subsequent decarboxylation to afford the optically pure methylphosphine oxides 40. Both transformations occurred in very high, often quantitative, yield. This method was an advance because, as seen before, the introduction of encumbered groups by the original Mislow method is cumbersome. Moreover, methylphosphine oxides 40 are key intermediates to prepare diphosphines of the DiPAMP family (see Scheme 2.11). The chemistry of Scheme 2.14 has been used much more recently by Hii and co-workers to prepare series of ami-nohydroxy phosphine oxide ligands by coupling the acid derived from 39 (R = t-Bu) with (-)-norephedrine and (S)-valinol. 

The reaction is fast and results in a mixture of isomeric sulfoxides in the ratio 2,0 (( ), This observation is in analogy with that of Mislow who studied this isomerization for a number of aliphatic sulfoxides and proposed the mechanism which includes formation of an intermediate with the structure of sulfur dichloride type. 

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